Hi We’re developing a platform using TF-M and would like to get some clarity on using FPU on Secure and Non-Secure side. The idea is to let NS application decide if it wants to use FPU.

Currently, we are enabling CONFIG_TFM_ENABLE_FP which means we’re setting CPACR.CP10, CPACR.CP11 and enabling NSACR.CP10, NSACR.CP11.

With this configuration:

1. Is it okay if SE perform some FP operation which would set CONTROL.FPCA and return to NSE (CPACR_NS.CP10 and CPACR_NS.CP11 are not set) while CONTROL.FPCA is still set? 2. With the above configuration, if NSE wants to use FPU, it simply needs to enable CPACR_NS.CP10 and CPACR_NS.CP11. Is this correct? 3. If SE doesn’t require FPU, we could simply enable CONFIG_TFM_ENABLE_CP10CP11 (CONFIG_TFM_ENABLE_FP is OFF) and NS app would still be able access FPU after enabling CPACR_NS bits? 4. There is a hard requirement for the -mfloat-abi to be consistent for S, NS and all the static libraries used?

Thank you in advance!

Best Saurabh Jain